In recent years, a spotlight has been casted on warming-up technology for quickly warming-up an internal, combustion engine of an automotive vehicle when starting an operation of the engine, in order not only to improve fuel consumption ratio but also to provide a comfortable air conditioning environment for the automotive vehicle.
The technology of this kind is known in the art, for example, as disclosed in International Patent Publication. No. WO 2011/042942. According to the prior art, a cooling system for an automotive vehicle has a first cooling-water circuit and a second cooling-water circuit. Cooling water is circulated in the first cooling-water circuit, wherein the cooling water passes through an inside of an internal combustion engine of the automotive vehicle. On the other hand, the cooling water is circulated in the second cooling-water circuit without passing through the engine.
According to the above prior art, a valve device is provided in order not only to reduce a flow amount of the cooling water circulating in the first cooling-water circuit when the valve device is closed but also to mix the cooling water of the first: cooling-water circuit with the cooling water of the second cooling-water circuit when the valve device is opened. The valve device is so controlled that an opening degree of a valve member thereof becomes smaller when temperature of the cooling water in the first cooling-water circuit is lower than a predetermined threshold value, which is used for determining a half warm-up condition of the engine. A quick warm-up process for the engine is thus carried out by making the opening degree of the valve member smaller and thereby reducing a flow amount of the cooling water circulating in the first cooling-water circuit.
In the cooling system of the above prior art, since the cooling water is heated by heat generated by the engine itself, a relatively long time is necessary until the temperature of the cooling water is increased since the engine operation is started. Therefore, it is a problem that it is not possible to sufficiently obtain an effect of quickly warming-up the engine.